Multi-driving device and driving circuit thereof

ABSTRACT

A driving circuit comprises three switch groups, each comprising a first switch, a second switch, a third switch and a fourth switch. The first and the second switches are coupled in series. The third switch is serially coupled to the fourth switch and coupled between the first and the second switches. An i th  inductor of a first driving device is coupled between the third and the fourth switches, wherein i ranges between 1˜3. In high speed mode, the first and the third switches of one of the switch groups are turned on, the second and the fourth switches are turned off, the first and the third switches of another of the switch groups are turned off, the second switch is turned on, and the fourth switch is turned on or off to raise voltage of the a driving device.

This application claims the benefit of Taiwan application Serial No.101140095, filed Oct. 30, 2012, the disclosure of which is incorporatedby reference herein in its entirety, and claims the benefit of Taiwanapplication Serial No. 102111726, filed Apr. 1, 2013, the disclosure ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosure relates in general to a driving circuit and amulti-driving device using the same, and more particularly to a drivingcircuit capable of improving its performance in a high speed and amulti-driving device using the same.

BACKGROUND

Normally, a conventional driving device consists of a high speed motorand a low speed motor to increase the performance at both low speed andhigh speed. However, when the conventional driving device is operated ina high speed, the driving device normally uses the high speed motoronly; hence, making the low speed motor idled. Therefore, when thedriving device is operated in a high speed, the low speed motor is likea dummy, and the use of the low speed motor is restricted.

SUMMARY

The disclosure is directed to a driving circuit and a multi-drivingdevice using the same. In an embodiment, the application of low speedmotor can be extended and the high speed performance of themulti-driving device can be improved.

According to one embodiment, a multi-driving device is provided. Themulti-driving device comprises a first driving device, a second drivingdevice and a driving circuit. The first driving device comprises ninductors. The driving circuit is coupled to the first driving deviceand the second driving device, and comprises n switch groups coupled inparallel, wherein n is a positive integer larger than 3. Each switchgroup comprises a first switch, a second switch, a third switch and afourth switch. The first switch and the second switch are coupled inseries. The third switch is serially coupled to the fourth switch andcoupled between the first switch and the second switch. An i^(th)inductor of the first driving device is coupled between the third switchand the fourth switch, wherein i ranges between 1 and n. In a low speedmode, each first switch and each second switch are turned on. In a highspeed mode, the first switch and the third switch of a first one of then switch groups are turned on, the second switch and the fourth switchof the first one of the n switch groups are turned off, the first switchand the third switch of a second one of the n switch groups are turnedoff, the second switch one of the second one of the n switch groups isturned on, and the fourth switch one of the second one of the n switchgroups is selectively turned on or off so as to raise the voltage of thesecond driving device.

According to another embodiment, a driving circuit is provided. Thedriving circuit is coupled to the first driving device and the seconddriving device. The first driving device comprises n inductors, whereinn is a positive integer larger than 3. The driving circuit comprises nswitch groups coupled in parallel. Each switch group comprises a firstswitch, a second switch, a third switch and a fourth switch. The firstswitch and the second switch are coupled in series. The third switch isserially coupled to the fourth switch and coupled between the firstswitch and the second switch. An i^(th) inductor of the first drivingdevice is coupled between the third switch and the fourth switch,wherein i ranges between 1 and n. In a low speed mode, each first switchand each second switch are turned on. In a high speed mode, the firstswitch and the third switch of a first one of the n switch groups areturned on, the second switch and the fourth switch of the first one ofthe n switch groups are turned off, the first switch and the thirdswitch of a second one of the n switch groups are turned off, the secondswitch of the second one of the n switch groups are turned on, and thefourth switch of the second one of the n switch groups is selectivelyturned on or off so as to raise the voltage of the second drivingdevice.

According to one embodiment, a multi-driving device is provided. Themulti-driving device comprises a first driving device, a second drivingdevice and a driving circuit. The first driving device comprises ninductors. The driving circuit is coupled to the first driving deviceand the second driving device and comprises n switch groups coupled inparallel, wherein each switch group comprises a first switch, a secondswitch, a third switch and a fourth switch, the first switch and thesecond switch are coupled in series, the third switch is seriallycoupled to the fourth switch and coupled between the first switch andthe second switch, an ith inductor of the first driving device iscoupled between the third switch and the fourth switch, and i rangesbetween 1 and n. In a low speed mode, the first switch and the secondswitch of a first one of the n switch groups are turned on, the firstswitch of a second one of the n switch groups is turned off, the secondswitch of the second one of the n switch groups is turned on, the firstswitch of a third one of the n switch groups is turned off, and thesecond switch of the third one of the n switch groups is turned on. in ahigh speed mode, the first switch of the first one of the n switchgroups is turned on, the second switch of the first one of the n switchgroups is turned off, the third switch of the first one of the n switchgroups is turned on, the fourth switch of the first one of the n switchgroups is turned off, the first switch of the second one of the n switchgroups is turned off, and the first switch of the third one of the nswitch groups is turned off; by controlling at least one of the fourthswitch of the second one of the n switch groups and the fourth switch ofthe third one of the n switch groups to be turned on or off through asignal, so as to raise the voltage of the second driving device.

According to another embodiment, a driving circuit is provided. Thedriving circuit is coupled to a first driving device and a seconddriving device and comprises n switch groups coupled in parallel,wherein each switch group comprises a first switch, a second switch, athird switch and a fourth switch, the first switch and the second switchare coupled in series, the third switch is serially coupled to thefourth switch and coupled between the first switch and the secondswitch, an ith inductor of the first driving device is coupled betweenthe third switch and the fourth switch, and i ranges between 1 and n. Ina low speed mode, the first switch and the second switch of a first oneof the n switch groups are turned on, the first switch of a second oneof the n switch groups is turned off, the second switch of the secondone of the n switch groups is turned on, the first switch of a third oneof the n switch groups is turned off, and the second switch of the thirdone of the n switch groups is turned on. in a high speed mode, the firstswitch of the first one of the n switch groups is turned on, the secondswitch of the first one of the n switch groups is turned off, the thirdswitch of the first one of the n switch groups is turned on, the fourthswitch of the first one of the n switch groups is turned off, the firstswitch of the second one of the n switch groups is turned off, and thefirst switch of the third one of the n switch groups is turned off; bycontrolling at least one of the fourth switch of the second one of the nswitch groups and the fourth switch of the third one of the n switchgroups to be turned on or off through a signal, so as to raise thevoltage of the second driving device.

The above and other aspects of the disclosure will become betterunderstood with regard to the following detailed description of thenon-limiting embodiment(s). The following description is made withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a functional block diagram of a multi-driving deviceaccording to an embodiment of the disclosure;

FIG. 1B shows a circuit diagram of the multi-driving device of FIG. 1A;

FIG. 1C shows a circuit diagram of a first switch group of FIG. 1B;

FIG. 2 shows an equivalent circuit diagram of a driving circuit when themulti-driving device of FIG. 1A is operated in a low speed;

FIG. 3A shows a current path diagram of a driving circuit when themulti-driving device of FIG. 1A is operated in a high speed and a fourthswitch is turned on;

FIG. 3B shows an equivalent circuit diagram of the driving circuit ofFIG. 3A;

FIG. 4A shows a current path diagram of a driving circuit when themulti-driving device of FIG. 1A is operated in a high speed and thefourth switch turned off;

FIG. 4B shows an equivalent circuit diagram of the driving circuit ofFIG. 4A;

FIG. 5 shows a control signal of the fourth switch according to anembodiment of the disclosure;

FIG. 6A shows a torque vs. rotation speed performance diagram of a firstdriving device and a second driving device of FIG. 1A;

FIG. 6B shows a torque vs. rotation speed synthetic performance diagramof the first driving device and the second driving device of FIG. 6A;

FIG. 7 shows a circuit diagram of a driving circuit of a multi-drivingdevice according to another embodiment of the disclosure;

FIG. 8 shows a circuit diagram of a multi-driving device according toanother embodiment of the disclosure;

FIG. 9 shows an equivalent circuit diagram of the driving circuit whenthe multi-driving device of FIG. 8 is operated in the low speed;

FIG. 10 shows an equivalent circuit diagram of the driving circuit whenthe multi-driving device of FIG. 8 is operated in the high speed;

FIG. 11A shows an equivalent circuit diagram of the driving circuit whenthe multi-driving device of FIG. 8 is operated in one control method ofthe high speed;

FIG. 11B shows a current path diagram of the driving circuit of FIG.11A;

FIG. 12A shows an equivalent circuit diagram of the driving circuit whenthe multi-driving device of FIG. 8 is operated in another control methodof the high speed;

FIG. 12B shows a current path diagram of the driving circuit of FIG.12A;

FIG. 13A shows an equivalent circuit diagram of the driving circuit whenthe multi-driving device of FIG. 8 is operated in another control methodof the high speed; and

FIG. 13B shows a current path diagram of the driving circuit of FIG.13A.

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

DETAILED DESCRIPTION

Referring to FIG. 1A, a functional block diagram of a multi-drivingdevice according to an embodiment of the disclosure is shown. Themulti-driving device 10, such as a transport, machine tool, or otherdevices requiring output power, comprises a first driving device 100, adriving circuit 200, a second driving device 300 and a driving circuit400.

Referring to FIG. 1B, a circuit diagram of the multi-driving device ofFIG. 1A is shown. The first driving device 100 is coupled to the seconddriving device 300 through the driving circuits 200 and 400. The firstdriving device 100, such as a three-phase motor, comprises a firstinductor L1, a second inductor L2 and a third inductor L3. The firstdriving device 100 can also be realized by a driving device comprisingan inductor. The variety of second driving device 300 can be similar tothat of the first driving device 100. Besides, the inductance of thesecond driving device 300 and that of the first driving device 100 canbe the same or different.

The driving circuit 200, coupled to the first driving device 100,comprises a first switch group 210, a second switch group 220 and athird switch group 230 which are coupled in parallel.

Referring to FIG. 1C, a circuit diagram of a first switch group of FIG.1B is shown. The first switch group 210 comprises a first switch S11 anda second switch S12, which are coupled in series, and a third switch S13and a fourth switch S14, which are coupled in series. The third switchS13 is coupled between the first switch S11 and the second switch S12,and the first inductor L1 of the first driving device 100 is coupledbetween the third switch S13 and the fourth switch S14.

Return to FIG. 1B. Like the first switch group 210, the second switchgroup 220 comprises a first switch S21 and a second switch S22, whichare coupled in series, and a third switch S23 and a fourth switch S24,which are coupled in series. The third switch S23 is coupled between thefirst switch S21 and the second switch S22, and the second inductor L2of the first driving device 100 is coupled between the third switch S23and the fourth switch S24.

As indicated in FIG. 1B, like the first switch group 210, the thirdswitch group 230 comprises a first switch S31 and a second switch S32,which are coupled in series, and a third switch S33 and a fourth switchS34, which are coupled in series. The third switch S33 is coupledbetween the first switch S31 and the second switch S32, and the thirdinductor L3 of the first driving device 100 is coupled between the thirdswitch S23 and the fourth switch S34.

In terms of the variety of switches, the first switch, the secondswitch, the third switch and the fourth switch are realized by such asrelays, metal oxide semiconductor field effect transistors (MOSFET),insulated gate bipolar transistors (IGBT) or other suitable switchcomponents. At least two of the first switch, the second switch, thethird switch and the fourth switch can have the same or differentvarieties. For example, the switches which are turned off (that is, thefirst switches S21 and S31 and the second switches S12 and S32) whenoperated in a high speed (elaborated below) can be realized by relays,and other switches can be realized by MOSFET, IGBT or a combinationthereof.

Referring to FIG. 2, an equivalent circuit diagram of a driving circuitwhen the multi-driving device of FIG. 1A is operated in a low speed isshown. When the multi-driving device is operated in a low speed, all ofthe first switches S11, S21 and S31 and all of the second switch S21,S22 and S32 are turned on, such that the circuit structure of thedriving circuit 200 of FIG. 2 is identical to the circuit structure ofthe driving circuit 400 for driving the second driving device 300. Thevoltage difference from node a to node b is equal to the voltagedifference from node c to node d. The input power (the voltagedifference from node c to node d) is directly transmitted to the drivingcircuit 400 through the driving circuit 200 so that the driving circuit400 can drive the second driving device 300 with the received inputpower.

Referring to FIG. 3A, a current path diagram of a driving circuit whenthe multi-driving device of FIG. 1A is operated in a high speed and afourth switch is turned on is shown. When the multi-driving device 10 isoperated in a high speed, in terms of the control of the first switchgroup 210, the first switch S11 and the third switch S13 are turned onand the second switch S12 and the fourth switch S14 are turned off; interms of the control of the second switch group 220, the first switchS21 and the third switch S23 are turned off, the second switch S22 isturned on, and the fourth switch S24 is selectively turned on or off.When the fourth switch S24 is turned on, as indicated in FIG. 3A, thecurrent path (denoted by bold lines) passes through the first switch S11and the third switch S13 of the first switch group 210, the firstinductor L1 and the second inductor L2 of the first driving device 100and the fourth switch S24 of the second switch group 220 for couplingthe first inductor L1 and the second inductor L2 in series.

Referring to FIG. 3B, an equivalent circuit diagram of the drivingcircuit of FIG. 3A is shown. When the multi-driving device 10 isoperated in a high speed and the fourth switch S24 is turned on, theinductor L′ is charged, wherein the inductance of the inductor L′ isequal to the equivalent inductance of the first inductor L1 and thesecond inductor L2 which are coupled in series.

Referring to FIG. 4A, a current path diagram of a driving circuit whenthe multi-driving device of FIG. 1A is operated in a high speed and thefourth switch turned off is shown. When the multi-driving device 10 isoperated in a high speed and the fourth switch S24 is turned off, thecurrent path (denoted by bold lines) passes through the first switch S11and the third switch S13 of the first switch group 210, the firstinductor L1 and the second inductor L2 of the first driving device 100,and the diode D23 of the third switch S23 and the second switch S22 ofthe second switch group 220 to raise the voltage of node a. Since thesecond driving device 300 is coupled to the driving circuit 200, thevoltage of the second driving device 300 can be raised. To put it ingreater details, due to the design of the driving circuit 200, thevoltage can be raised through the inductor of the first driving device100, so that the second driving circuit 400 can be provided with ahigher voltage for driving the second driving device 300 and increasingits rotation speed when the second driving device 300 is operated in ahigh speed mode.

Referring to FIG. 4B, an equivalent circuit diagram of the drivingcircuit of FIG. 4A is shown. When the multi-driving device 10 isoperated in a high speed and the fourth switch S24 is turned off, aninductor L′ charges the driving circuit 400 and raises its voltage.Meanwhile, the voltage difference from node a and node b is larger thanthe voltage difference from node c and node d. The driving circuit 400drives the second driving device 300 with the voltage-raised power.

Referring to FIG. 5, a control signal of the fourth switch according toan embodiment of the disclosure is shown. Whether the fourth switch S24is turned on or off is controlled by a pulse-width modulation (PWM)signal. The voltage Vab is determined by the pulse-width proportion Pand the voltage Vcd as illustrated in formulas (1). The pulse-widthproportion P denotes the proportion of the pulse-width D to the period T(P=D/T). The voltage Vcd denotes the voltage difference from node c andnode d and is realized by such as the battery voltage of themulti-driving device 10. The voltage Vab denotes the voltage differencenode a to node b.Vab=Vcd/(1−P)  (1)

Referring to FIGS. 6A and 6B. FIG. 6A shows a torque vs. rotation speedperformance diagram of a first driving device and a second drivingdevice of FIG. 1A. FIG. 6B shows a torque vs. rotation speed syntheticperformance diagram of the first driving device and the second drivingdevice of FIG. 6A. As indicated in FIG. 6A, curve C1 represents thetorque vs. rotation speed performance curve of the first driving device100, and curve C2 represents the torque vs. rotation speed performancecurve of the second driving device 300. In the present example, thefirst driving device 100 is exemplified by a low speed motor, and thesecond driving device 300 is exemplified by a high speed motor. When thedriving circuit 200 is omitted, curves C1 and C2 are combined as curveC12 of FIG. 6B. When the multi-driving device 10 uses the drivingcircuit 200, curves C1 and C2 are combined as curve C12′ of FIG. 6B. Itis evident that the rotation speed of the multi-driving device 10operated in a high speed mode is further increased.

In the above embodiments, the current path passes through the firstswitch group 210 and the second switch group 220 for coupling the firstinductor L1 and the second inductor L2 in series. However, the currentpath may pass through any two of the first switch group 210, the secondswitch group 220 and the third switch group 230 for coupling twocorresponding inductors in series as long as the following conditionsare satisfied: (1) the first switch and the third switch of one of thefirst switch group 210, the second switch group 220 and the third switchgroup 230 are turned on, and the second switch and the fourth switch areturned off; (2) the first switch and the third switch of another of thefirst switch group 210, the second switch group 220 and the third switchgroup 230 are turned off, the second switch is turned on, and the fourthswitch is selectively turned on or off.

Referring to FIG. 7, a circuit diagram of a driving circuit of amulti-driving device according to another embodiment of the disclosureis shown. In the present example, the driving circuit 200 is coupled tothe first driving device 100, and comprises n switch groups coupled inparallel, wherein n is a positive integer equal to or larger than 3. Forexample, the driving circuit 200 comprises a first switch group 210, asecond switch group 220, . . . , an i^(th) switch group 200 i, . . . ,and an n^(th) switch group 200 n. The first driving device 100 isrealized by such as an n-phase motor for coupling each switch group ofthe driving circuit 200.

As indicated in FIG. 7, the i^(th) switch group 200 i comprises a firstswitch Si1, a second switch Si2, a third switch Si3 and a fourth switchSi4. The first switch Si1 and the second switch Si2 are coupled inseries, the third switch Si3 is serially coupled to the fourth switchSi4 and coupled between the first switch Si1 and the second switch Si2,wherein i ranges between 1 and n. In an example, the first switch group210 comprises a first switch S11, a second switch S12, a third switchS13 and a fourth switch S14, wherein the first switch S11 and the secondswitch S12 are coupled in series, the third switch S13 is seriallycoupled to the fourth switch S14 and coupled between the first switchS11 and the second switch S12. In another example, the n^(th) switchgroups 200 n comprises a first switch Sn1, a second switch Sn2, a thirdswitch Sn3 and a fourth switch Sn4, wherein the first switch Sn1 and thesecond switch Sn2 are coupled in series, and the third switch Sn3 isserially coupled to the fourth switch Sn4 and coupled between the firstswitch Sn1 and the second switch Sn2.

As indicated in FIG. 7, an inductor of the first driving device 100 iscoupled between the third switch Si3 and the fourth switch Si4 of thei^(th) switch group 200 i, wherein i ranges between 1 and n. In anexample, the first inductor of the first driving device 100 is coupledbetween the third switch S13 and the fourth switch S14 of the firstswitch group 210. In another example, the n^(th) inductor of the firstdriving device 100 is coupled between the third switch Sn3 and thefourth switch Sn4 of the n^(th) switch groups 200 n.

For the driving circuit of another embodiment, in a low speed mode, thefirst switch and the second switch the first one of the n switch groupsare turned on, the first switch of the second one of the n switch groupsis turned off, the second switch of the second one of the n switchgroups is turned on, the first switch of the third one of the n switchgroups is turned off, and the second switch of the third one of the nswitch groups is turned on. In a high speed mode, the first switch ofthe first one of the n switch groups is turned on, the second switch ofthe first one of the n switch groups is turned off, the third switch ofthe first one of the n switch groups is turned on, the fourth switch ofthe first one of the n switch groups is turned off, the first switch ofthe second one of the n switch groups is turned off, and the firstswitch of the third one of the n switch groups is turned off; bycontrolling at least one of the fourth switch of the second one of the nswitch groups and the fourth switch of the third one of the n switchgroups to be turned on or off through a signal, so as to raise thevoltage of the second driving device. Some embodiments are disclosedbelow for elaborating.

Referring to FIG. 8, a circuit diagram of a multi-driving deviceaccording to another embodiment of the disclosure is shown. Amulti-driving device 10′, such as a transport, machine tool, or otherdevices requiring output power, comprises a first driving device 100,the driving circuit 200′, the second driving device 300 and the drivingcircuit 400. In comparison with the above driving circuit, whether thedriving circuit of present embodiment is in the low speed mode or in thehigh speed mode, the first switch S11 of the first switch group 210 isturned on, the first switch S21 of the second switch group 220 is turnedoff, the first switch S21 of the third switch group 230 is turned off,and other switch can be turned on or off depends on the low speed modeor the high speed mode.

Referring to FIG. 9, an equivalent circuit diagram of the drivingcircuit when the multi-driving device of FIG. 8 is operated in the lowspeed. When the multi-driving device 10′ is operated in the low speed,the first switch S11 and the second switch S12 of the first switch group210 are turned on, the first switch S21 of the second switch group 220is turned off, the second switch S22 of the second switch group 220 isturned on, the first switch S31 of the third switch group 230 is turnedoff, and the second switch S32 of the third switch group 230 is turnedon. As a result, the circuit structure of the driving circuit 200′ isequivalent to that of the driving circuit 400 of the second drivingdevice 300, wherein the voltage difference from node a to node b isequal to the voltage difference from node c to node d. The input power(the voltage difference from node c to node d) is directly transmittedto the driving circuit 400 through the driving circuit 200 so that thedriving circuit 400 can drive the second driving device 300 with thereceived input power.

Referring to FIG. 10, an equivalent circuit diagram of the drivingcircuit when the multi-driving device of FIG. 8 is operated in the highspeed. When the multi-driving device 10′ is operated in the high speed,the first switch S11 of the first switch group 210 is turned on, thesecond switch S12 of the first switch group 210 is turned off, the thirdswitch S13 of the first switch group 210 is turned on, the fourth switchS14 of the first switch group 210 is turned off, the first switch S21 ofthe second switch group 220 is turned off, the first switch S31 of thethird switch group 230 is turned off, the fourth switch S24 of thesecond switch group 220 and the fourth switch S34 of the third switchgroup 230 are controlled by PWMs, so as to raise the voltage of thesecond driving device 300. Different current property can be obtained byat least one of the fourth switch S24 of the second switch group 220 andthe fourth switch S34 of the third switch group 230. Some embodimentsare disclosed below for elaborating.

Referring to FIGS. 11A and 11B, wherein FIG. 11A shows an equivalentcircuit diagram of the driving circuit when the multi-driving device ofFIG. 8 is operated in one control method of the high speed, and FIG. 11Bshows a current path diagram of the driving circuit of FIG. 11A. Inpresent embodiment, (1). the fourth switch S34 (illustrated in FIG. 8)of the third switch group 230 is always turned off, and at least one ofthe second switch S32 (illustrated in FIG. 8) and the third switch S33(illustrated in FIG. 8) of the third switch group 230 is always turnedoff, such that a circuit between the third inductor L3 and node a isopen; (2) the fourth switch S24 of the second switch group 220 iscontrolled to periodically turned on or off by a PWM P1 (illustrated inFIG. 11B); (3). the second switch S22 and the third switch S23 of thesecond switch group 220 are simultaneously turned off, such that a diodeD22 of the second switch S22 are serially connected to a diode D23 ofthe third switch S23 between node a and the fourth switch S24. As aresult, a current I2 transmitted between the first inductor L1 and thesecond inductor L2 can be obtained. In another embodiment, only one ofthe second switch 822 and the third switch S23 of the second switchgroup 220 is turned off, and another of the second switch S22 and thethird switch S23 of the second switch group 220 can be turned on or off,such that only one of the diode D23 of the second switch S22 and thediode D23 of the third switch S23 is coupled to between the node a andthe fourth switch S24. In comparison with the diode D22 and D23 areserially connected between the node a and the fourth switch S24, theresistance is reduced since only one of the diode D22 and D23 is coupledto between the node a and the fourth switch S24. In another embodiment,different distribution of the current I2 can be obtained by changingwaveform and/or phase of the PWM P1. Referring to FIGS. 12A and 12B,wherein FIG. 12A shows an equivalent circuit diagram of the drivingcircuit when the multi-driving device of FIG. 8 is operated in anothercontrol method of the high speed, and FIG. 12B shows a current pathdiagram of the driving circuit of FIG. 12A. In present embodiment, (1).the fourth switch S24 (illustrated in FIG. 8) of the second switch group220 is always turned off, and at least one of the second switch S22(illustrated in FIG. 8) and the third switch S23 (illustrated in FIG. 8)of the second switch group 220 is always turned off, such that a circuitbetween the second inductor L2 and the node a is open; (2) the fourthswitch S34 of the third switch group 230 is controlled to periodicallyturned on or off by a PWM P2 (illustrated in FIG. 12B); (3). the secondswitch S32 and the third switch S33 of the third switch group 230 aresimultaneously turned off, such that a diode D32 of the second switchS32 are serially connected to a diode D33 of the third switch S33between node a and the fourth switch S24. As a result, a current I3transmitted between the first inductor L1 and the third inductor L3 canbe obtained. In another embodiment, only one of the second switch 32 andthe third switch S33 of the third switch group 230 is turned off, andanother of the second switch S32 and the third switch S33 of the thirdswitch group 230 can be turned on or off, such that only one of thediode D32 of the second switch S32 and the diode D33 of the third switchS33 is coupled to between the node a and the fourth switch S34. Incomparison with the diode D32 and D33 are serially connected between thenode a and the fourth switch S34, the resistance is reduced since onlyone of the diode D32 and D33 is coupled to between the node a and thefourth switch S34. In another embodiment, different distribution of thecurrent I3 can be obtained by changing waveform and/or phase of the PWMP2.

Referring to FIGS. 13A and 13B, wherein FIG. 13A shows an equivalentcircuit diagram of the driving circuit when the multi-driving device ofFIG. 8 is operated in another control method of the high speed, and FIG.13B shows a current path diagram of the driving circuit of FIG. 13A. Inpresent embodiment, the fourth switch S24 of the second switch group 220is periodically turned on or off by the PWM P1 (illustrated in FIG.11B), and the fourth switch S34 of the third switch group 230 isperiodically turned on or off by the PWM P2 (illustrated in FIG. 12B),simultaneously. The control of other switch S22 and S23 are similar tothat disclosed in FIG. 11A, the control of other switch S32 and S33 aresimilar to that disclosed in FIG. 12A, and the similarities are notrepeated here. If a phase difference between the PWMs P1 and P2 is 180degrees, the current I2 transmitted between the first inductor L1 andthe second inductor L2 and the current I3 transmitted between the firstinductor L1 and the third inductor L3 converges as a current It, asillustrated in FIG. 13B.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodiments.It is intended that the specification and examples be considered asexemplary only, with a true scope of the disclosure being indicated bythe following claims and their equivalents.

What is claimed is:
 1. A multi-driving device, comprising: a firstdriving device comprising n inductors, wherein n is a positive integerequal to or larger than 3; a second driving device; and a drivingcircuit coupled to the first driving device and the second drivingdevice and comprising n switch groups coupled in parallel, wherein eachswitch group comprises a first switch, a second switch, a third switchand a fourth switch, the first switch and the second switch are coupledin series, the third switch is serially coupled to the fourth switch andcoupled between the first switch and the second switch, an i^(th)inductor of the first driving device is coupled between the third switchand the fourth switch, and i ranges between 1 and n; wherein, in a lowspeed mode, each first switch and each second switch are turned on; in ahigh speed mode, the first switch and the third switch of a first one ofthe n switch groups are turned on, the second switch and the fourthswitch of the first one of the n switch groups are turned off, the firstswitch and the third switch of a second one of the n switch groups areturned off, the second switch of the second one of the n switch groupsis turned on, and the fourth switch of the second one of the n switchgroups is selectively turned on or off so as to raise the voltage of thesecond driving device.
 2. The multi-driving device according to claim 1,wherein the fourth switch of the second one of the n switch groups iscontrolled by a pulse-width modulation (PWM) signal.
 3. Themulti-driving device according to claim 1, wherein the first switch, thesecond switch, the third switch and the fourth switch of each switchgroup are realized by relays, metal oxide semiconductor field effecttransistors or insulated gate bipolar transistors.
 4. The multi-drivingdevice according to claim 1, wherein the first switches and the secondswitches which are turned off are realized by relays.
 5. Themulti-driving device according to claim 1, wherein the first drivingdevice and the second driving device are realized by motors.
 6. Adriving circuit coupled to a first driving device and a second drivingdevice, wherein the first driving device comprises n inductors, n is apositive integer equal to or larger than 3, and the driving circuitcomprises: n switch groups coupled in parallel, wherein each switchgroup comprises a first switch, a second switch, a third switch and afourth switch, the first switch and the second switch are coupled inseries, the third switch is serially coupled to the fourth switch andcoupled between the first switch and the second switch, an i^(th)inductor of the first driving device is coupled between the third switchand the fourth switch, and, i ranges between 1 and n; wherein, in a lowspeed mode, each first switch and each second switch are turned on; in ahigh speed mode, the first switch and the third switch of a first one ofthe n switch groups are turned on, the second switch and the fourthswitch of the first one of the n switch groups are turned off, the firstswitch and the third switch of a second one of the n switch groups areturned off, the second switch of the second one of the n switch groupsis turned on, and the fourth switch of the second one of the n switchgroups is selectively turned on or off so as to raise the voltage of thesecond driving device.
 7. The driving circuit according to claim 6,wherein the fourth switch of the second one of the n switch groups iscontrolled by a PWM signal.
 8. The driving circuit according to claim 6,wherein the first switch, the second switch, the third switch and thefourth switch of each switch group are realized by relays, metal oxidesemiconductor field effect transistors or insulated gate bipolartransistors.
 9. The driving circuit according to claim 6, wherein, thefirst switches and the second switches which are turned off are realizedby relays.
 10. The driving circuit according to claim 6, wherein, thefirst driving device and the second driving device are realized bymotors.
 11. A multi-driving device, comprising: a first driving devicecomprising n inductors, wherein n is a positive integer equal to orlarger than 3; a second driving device; and a driving circuit coupled tothe first driving device and the second driving device and comprising nswitch groups coupled in parallel, wherein each switch group comprises afirst switch, a second switch, a third switch and a fourth switch, thefirst switch and the second switch are coupled in series, the thirdswitch is serially coupled to the fourth switch and coupled between thefirst switch and the second switch, an i^(th) inductor of the firstdriving device is coupled between the third switch and the fourthswitch, and i ranges between 1 and n; wherein, in a low speed mode, thefirst switch and the second switch of a first one of the n switch groupsare turned on, the first switch of a second one of the n switch groupsis turned off, the second switch of the second one of the n switchgroups is turned on, the first switch of a third one of the n switchgroups is turned off, and the second switch of the third one of the nswitch groups is turned on; in a high speed mode, the first switch ofthe first one of the n switch groups is turned on, the second switch ofthe first one of the n switch groups is turned off, the third switch ofthe first one of the n switch groups is turned on, the fourth switch ofthe first one of the n switch groups is turned off, the first switch ofthe second one of the n switch groups is turned off, and the firstswitch of the third one of the n switch groups is turned off; bycontrolling at least one of the fourth switch of the second one of the nswitch groups and the fourth switch of the third one of the n switchgroups to be turned on or off through a signal, so as to raise thevoltage of the second driving device.
 12. The multi-driving deviceaccording to claim 11, wherein a phase difference between a PWM signalfor controlling the fourth switch of the second one of the n switchgroups and a PWM signal for controlling the fourth switch of the thirdone of the n switch groups is 180 degrees.
 13. The multi-driving deviceaccording to claim 11, wherein the fourth switch of the second one ofthe n switch groups is always turned off, at least one of the secondswitch and the third switch of the second one of the n switch groups isalways turned off, the fourth switch of the third one of the n switchgroups is controlled by a PWM, one of the second switch and the thirdswitch of the third one of the n switch groups is turned off, andanother of the second switch and the third switch of the third one ofthe n switch groups is turned on or off.
 14. The multi-driving deviceaccording to claim 11, wherein the fourth switch of the third one of then switch groups is always turned off, at least one of the second switchand the third switch of the third one of the n switch groups is alwaysturned off, the fourth switch of the second one of the n switch groupsis controlled by a PWM, one of the second switch and the third switch ofthe second one of the n switch groups is turned off, and another of thesecond switch and the third switch of the second one of the n switchgroups is turned on or off.
 15. The multi-driving device according toclaim 11, wherein when the fourth switch of the second one of the nswitch groups and the fourth switch of the third one of the n switchgroups are controlled by PWMs, one of the second switch and the thirdswitch of the second one of the n switch groups is turned off, anotherof the second switch and the third switch of the second one of the nswitch groups is turned on or off, one of the second switch and thethird switch of the third one of the n switch groups is turned off, andanother of the second switch and the third switch of the third one ofthe n switch groups is turned on or off.
 16. A driving circuit coupledto a first driving device and a second driving device, wherein the firstdriving device comprises n inductors, and n is a positive integer equalto or larger than 3 and the driving circuit comprises: n switch groupscoupled in parallel, wherein each switch group comprises a first switch,a second switch, a third switch and a fourth switch, the first switchand the second switch are coupled in series, the third switch isserially coupled to the fourth switch and coupled between the firstswitch and the second switch, an i^(th) inductor of the first drivingdevice is coupled between the third switch and the fourth switch, and iranges between 1 and n; wherein, in a low speed mode, the first switchand the second switch of a first one of the n switch groups are turnedon, the first switch of a second one of the n switch groups is turnedoff, the second switch of the second one of the n switch groups isturned on, the first switch of a third one of the n switch groups isturned off, and the second switch of the third one of the n switchgroups is turned on; in a high speed mode, the first switch of the firstone of the n switch groups is turned on, the second switch of the firstone of the n switch groups is turned off, the third switch of the firstone of the n switch groups is turned on, the fourth switch of the firstone of the n switch groups is turned off, the first switch of the secondone of the n switch groups is turned off, and the first switch of thethird one of the n switch groups is turned off; by controlling at leastone of the fourth switch of the second one of the n switch groups andthe fourth switch of the third one of the n switch groups to be turnedon or off through a signal, so as to raise the voltage of the seconddriving device.
 17. The driving circuit according to claim 16, wherein aphase difference between a PWM signal for controlling the fourth switchof the second one of the n switch groups and a PWM signal forcontrolling the fourth switch of the third one of the n switch groups is180 degrees.
 18. The driving circuit according to claim 16, wherein thefourth switch of the second one of the n switch groups is always turnedoff, at least one of the second switch and the third switch of thesecond one of the n switch groups is always turned off, the fourthswitch of the third one of the n switch groups is controlled by a PWM,one of the second switch and the third switch of the third one of the nswitch groups is turned off, and another of the second switch and thethird switch of the third one of the n switch groups is turned on oroff.
 19. The driving circuit according to claim 16, wherein the fourthswitch of the third one of the n switch groups is always turned off, atleast one of the second switch and the third switch of the third one ofthe n switch groups is always turned off, the fourth switch of thesecond one of the n switch groups is controlled by a PWM, one of thesecond switch and the third switch of the second one of the n switchgroups is turned off, and another of the second switch and the thirdswitch of the second one of the n switch groups is turned on or off. 20.The driving circuit according to claim 16, wherein when the fourthswitch of the second one of the n switch groups and the fourth switch ofthe third one of the n switch groups are controlled by PWMs, one of thesecond switch and the third switch of the second one of the n switchgroups is turned off, another of the second switch and the third switchof the second one of the n switch groups is turned on or off, one of thesecond switch and the third switch of the third one of the n switchgroups is turned off, and another of the second switch and the thirdswitch of the third one of the n switch groups is turned on or off.